I. Field of the Invention
This invention relates generally to the manufacture of implantable medical devices, such as cardiac rhythm management devices and neural stimulators, and more particularly to a method and apparatus for hermetically sealing electrical circuitry within a metal housing.
II. Discussion of the Prior Art
The typical implantable medical tissue stimulating device comprises a battery-powered pulse generator and a microprocessor-based controller within a hermetically sealed metal housing commonly referred to as the “can”. The can generally comprises first and second halves that are joined together in a laser-welding operation about their perimeters after the battery power supply and electronic circuitry are inserted in the space defined by the two halves of the can. During the welding operation, a feed-through assembly is also welded in place on the can's header. The feed-through assembly includes a plurality of conductive wires extending through glass-to-metal seals so that electrical signals and stimulating pulses may be applied to and conveyed from the encased circuitry to terminal contacts within a lead connector block affixed to the outer surface of the header.
During the laser welding of the can, gases, notably argon and helium, are utilized. This gaseous atmosphere is subject to high voltage breakdown which can be detrimental to proper operation of the medical device. Thus, it is necessary to exhaust these gases from the can and replace them with a more inert gas exhibiting a significantly higher electrical breakdown resistance.
In accordance with prior art approaches, device backfilling with the inert gas has been done using tube stems that are located either on the feed-through assembly or on the case halves. The undesirable argon and helium are then exhausted through this tube and once exhausted, the interior of the can is backfilled with the inert gas, such as nitrogen. A small ball is then dropped into the tube to create a temporary seal, with the ball ultimately being welded in place. The tube stem utilized is relatively tall and thus necessarily increases the size and cost of the feed-through and the resulting implantable device. The size of the stem also may effect the available location of the feed-through in the device as well as the location of components that must be placed proximate the feed-through area due to arcing concerns. Furthermore, the routing of the feed-through wires is further complicated by the location of the tubular backfill stem in that the wires must be routed a safe distance away from the tube in order to prevent arcing. It is, therefore, desirable to provide a backfill approach allowing placement in an area of the header such that it does not interfere with other components or wire routing and which eliminates any arcing concerns.
As the complexity of implantable medical devices increases, there is an attendant increase in the number of feed-through wires required and thus, space on the feed-through is at a premium. It is therefore advantageous if the backfill tube can be eliminated from the feed-through assembly and the header.
It has also been a practice in the past to mechanically affix the lead connector block to the can's header using a suitable bonding agent. To hold the lead connector in place while the bonding agent cures, it has also been the practice to provide one or more anchors on the can's header which fit into preformed sockets in the base of the lead connector block. In order to accurately place the lead connector block anchors, it has been necessary to employ fixturing to accurately locate the anchor on the header prior to its being welded to the header. This fixturing necessarily increases the manufacturing costs.
The present invention provides a manufacturing method which dispenses with the need for a backfill tube on the header of the device housing by redesigning the anchor used in securing a lead connector block to the device's header. The anchor employed does not require the use of fixturing to properly position it on the device header prior to its being welded in place.